An auto focusing (AF) system is commonly installed in a photographing apparatus such as a digital compact camera, a lens interchangeable camera, a camcorder, or the like. The AF system may be classified into a phase difference detecting type AF system (hereinafter referred to as a phase difference AF system) and a contrast detecting type AF system (hereinafter referred to as a contrast AF system).
The phase difference AF system includes a phase difference AF sensor separately from an imaging device and acquires a defocusing amount of a lens from an output of the phase difference AF sensor to perform AF. The phase difference AF system includes an additional mirror for phase difference AF. For example, besides a main mirror, a sub mirror that guides incident light to the phase difference AF sensor is installed to apply the phase difference AF to a digital single lens reflection (DSLR) camera. The phase difference AF system performs high-speed and high-performance AF but includes an additional optical system for the phase difference AF. Therefore, the phase difference AF system is a high cost system.
The contrast AF system extracts high frequency data from an image data output of the image device and performs AF control to improve the high frequency data.
The contrast AF system includes a signal processing circuit for the high frequency data but does not include an additional sensor or optical system. Therefore, the contrast AF system is relatively inexpensive to manufacture. However, the contrast AF system performs AF at lower speed and precision than the phase difference AF system.